Can Eccentric Reducer Be on Pump Discharge?

2/6/2023

For a fire pump subject to NFPA 20, I know that the suction side requires an eccentric reducer, but “can” one be put on the discharge side?

I have a situation where we are removing and replacing existing pumps where both the suction and discharge are at the same elevation, but the new pumps have the discharge about 2.5” lower than the suction.

I am trying to find a solution to resolve this. Thanks in advance.

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9 Comments

Dan Wilder

2/6/2023 06:38:43 am

There are no requirements for a concentric or eccentric increaser for the discharge side of a pump, or even the orientation of that eccentric fitting.

Section 4.17 of NFPA 20 (22' in my case) has the requirements for the discharge fittings, none of which include specific fittings for pipe size changes on the discharge side.

Glenn Berger

2/6/2023 08:07:50 am

Eccentric reducer (increaser) can be used on the discharge of a fire pump.

Alex

2/6/2023 08:54:02 am

Yes, an eccentric reducer can be used on the discharge of the pump.

NFPA 20, 2013, Section 4.15 Discharge Pipe and Fittings does not mention omitted fittings.

4.15.2 states that the pressure rating of the discharge components must be adequate for the maximum total discharge head with the pump operating at shutoff and rated speed but must not be less than the rating of the fire protection system.

Cliff Schulze

2/6/2023 09:13:53 am

While it seems you can use an eccentric reducer on the discharge side of the fire pump, Your options to make up 2 1/2" are very limited. In fact my book indicates the only commercially available fitting with the 2 1/2" vertical difference is an 8" x 3".

I suppose it's possible there is a fabricator that can make one.

Dwight H Havens

2/6/2023 09:19:51 am

I think that this is a great question because it allows us the opportunity to understand why there is a difference between the need for an eccentric reducer on the suction side vice either on the discharge side. Think about it, then comment.

Franck

2/6/2023 04:32:43 pm

The answer is cavitation and early aging of the pump’s impeller.
Concentric reduction on suction side brings turbulences too close to the pump casing. You could have a concentric reduction on the suction side if it was far enough. As for butterfly valve on the suction side.
On the discharge side, you don’t have this issue anymore !
And by the way, be aware that the eccentric reduction at the bottom side is when the suction pipe is coming from below the pump casing level (or same level). When the suction pipe is coming from above (vertical line then elbow), then the eccentric side is to be put on top !

Jesse

2/6/2023 09:43:34 am

Yep you can indeed use a neccentreic reducer on the discharge side of the pump

Mark Harris

2/7/2023 02:12:21 pm

Franck thanks for sharing the comment about the eccentric reducer orientation when supply is from higher elevation. Been doing this over 40 years and was not aware of that.

Franck

2/9/2023 09:26:39 am

You can check

https://www.enggcyclopedia.com/2011/12/pumps-suction-piping-eccentric-reducers-straight-lengths-piping/

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Can Eccentric Reducer Be on Pump Discharge?

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